The present invention relates to a substrate transport container suitable for use in storing or transporting objects, e.g. semiconductor wafers, photomasks, or hard disks, in an atmosphere of extremely high cleanliness.
During transport or storage of substrates, e.g. semiconductor wafers or photomasks, produced in a semiconductor manufacturing factory, for example, if traces of dust or gaseous impurities present in the surrounding air adhere to the semiconductor wafers or other objects, the product yield is lowered. This tendency becomes increasingly remarkable as the degree of integration increases. In the field of magnetic disks also, recording has been becoming denser acceleratedly since the advent of magnetoresistive heads. Accordingly, there has been a demand for high cleanliness regarding not only dust but also gaseous impurities.
To produce a clean space for accommodating substrates when transport stored, clean box and so forth equipped with a fan motor, an HEPA (high efficiency particle air) filter and a ULPA (ultra low penetration air) filter have been developed. As a technique of locally cleaning the periphery of semiconductor wafers, for example, there is a method wherein the atmosphere in a clean box accommodating semiconductor wafers is replaced with high-purity nitrogen to maintain cleanliness and to suppress the growth of a native oxide film.
However, the clean box using an HEPA filter and a ULPA filter cannot remove traces of organic or inorganic gases although it is capable of removing particulate contaminants. Moreover, if a large amount of circulating air flows through a part that does not directly contribute to cleaning of objects being transported or stored, or if there is an area where the circulating air undesirably stays in the clean box, it is impossible to expect an improvement in the ventilation efficiency in the clean box.
Consequently, the contamination preventing effect by the cleaned air deteriorates. With the method wherein the atmosphere in the clean box is replaced with high-purity nitrogen, it is impossible to remove impurities generated from the component parts in the container and the semiconductor wafers themselves. In addition, the use of nitrogen involves a problem in terms of safety.
Also, in the semiconductor manufacturing industry, silicon wafers are rapidly increasing in diameter, and circuit patterns formed thereon are becoming increasingly small and fine. As the diameter of wafers increases, the size and weight of a container used to transport them also increase. Consequently, it is becoming difficult to handle wafer transport containers by manual operation. In addition, as integrated circuits become smaller and finer, it is necessary to isolate wafers from human beings as the main source of contamination in the semiconductor manufacturing factory. That is, it is essential to transport wafers using a machine and to open and close the transport container door mechanically.
In view of the above-described problems, an object of the present invention is to provide a substrate transport container which is not only capable of efficiently preventing substrates accommodated therein from being contaminated by an ambient atmosphere but which is also capable of effectively preventing contamination of the substrates with contaminants generated from the substrates themselves and the component parts in the container, and which allows an automated operation in the factory.
According to a first aspect of the present invention, there is provided a substrate transport container having a carrier box including a container body and a door hermetically sealably covering an opening provided in the front of the container body. Partitions are provided to form a circulating flow path in the carrier box. The circulating flow path has a flow path in which air flows toward substrates and a flow path in which air flows toward a fan. A substrate carrying section is disposed in the flow path in which air flows toward the substrates to carry the substrates in such a way that the principal surfaces of the substrates are approximately parallel to the flow path in which air flows toward the substrates. A particle removing filter and a gaseous impurity trapping filter are placed on the upstream side of the substrate carrying section in the flow path in which air flows toward the substrates. A fan motor is incorporated in the carrier box to form an air current which circulates through the circulating flow path.
Thus, a circulating air current is formed in the carrier box, and the circulating air is sent to the substrate carrying section after being cleaned physically and chemically through the particle removing filter and the gaseous impurity trapping filter. Accordingly, even if the container contains particles likely to adhere to the inner walls of the container or the substrates or contains contaminants source such as gases generated from the container, the particles or gases are prevented from contaminating the substrates held in the substrate carrying section. In addition, because the wafer loading/unloading door is located on the downstream side of the substrate carrying section, the substrates are prevented from being contaminated through the container portions, which is likely to be contaminated when the door is opened or closed.
SEMI (Semiconductor Equipment and Materials International) Standards are known as international standards relating to semiconductor manufacturing equipment and materials. The SEMI Standards specify items relating to the standard interfaces of transport containers for 200-mm wafers, 300-mm wafers and so forth. The structure having an opening provided in a side of the container body is adapted to the front-opening interface specified for 300-mm wafer transport containers.
As a membrane material for the gaseous impurity trapping filter, it is possible to use, for example, ion-exchange nonwoven fabric or fiber, activated carbon fiber, granular activated carbon, pulverized activated carbon, or granular silicon singly or in combination, or an integrated material obtained by laminating these materials. Ammonia and other ions present in the air and ionic substances contained in mist, e.g. hydrofluoric acid and hydrochloric acid, can be efficiently adsorbed and thus removed by ion-exchange nonwoven fabric or fiber and activated carbon fiber obtained by carbonizing and activating cellulosic fiber, acrylic fiber and lignin fiber. Ion-exchange nonwoven fabric or fiber produced by radiation-induced graft polymerization reaction can be used.
According to a second aspect of the present invention, there is provided a substrate transport container having a carrier box including a container body and a door hermetically sealably covering an opening provided in the bottom of the container body. Partitions are provided to form a circulating flow path in the carrier box. The circulating flow path has a flow path in which air flows toward substrates and a flow path in which air flows toward a fan. A substrate carrying section is disposed in the flow path in which air flows toward the substrates to carry the substrates in such a way that the principal surfaces of the substrates are approximately parallel to the flow path in which air flows toward the substrates. A particle removing filter and a gaseous impurity trapping filter are placed on the upstream side of the substrate carrying section in the flow path in which air flows toward the substrates. A fan motor is incorporated in the carrier box to form an air current which circulates through the circulating flow path.
This substrate transport container differs from the substrate transport container according to the first aspect of the present invention in that a door is provided at the bottom of the container. This is because, in accordance with SEMI Standards, the standard mechanical interface of transport containers for wafers which is not larger than 200 millimeters in diameter has a structure in which the container bottom is opened and closed.
In the substrate transport containers according to the first and second aspects of the present invention, the door may have an automatic open-close latch mechanism. With this arrangement, when the substrate transport container is seated on a delivery station or the like that provides a place for delivery of substrates for the substrate transport container, the door is automatically opened, and thus delivery can be performed speedily.
According to a third aspect of the present invention, there is provided a combination of a substrate transport container according to the first or second aspect of the present invention and an automatic door opener for automatically opening and closing a wafer loading/unloading door of the substrate transport container. The automatic door opener has charging terminals for automatically charging a secondary battery of the substrate transport container when it is placed on the automatic door opener. As automation of semiconductor manufacturing factories advances, it will become necessary to automate the charging of a secondary battery as a power source for driving the fan motor. The substrate transport containers generally positioned at the automatic door opener for automatically opening and closing a wafer loading/unloading door of the substrate transport container for loading and unloading wafers into and from semiconductor manufacturing equipment. When the substrate transport container is placed on the automatic door opener, the secondary battery is automatically charged, thereby allowing the fan motor to be operated and controlled continuously for a long period of time without manual operation.
According to a fourth aspect of the present invention, there is provided a combination of a substrate transport container according to the first or second aspect of the present invention and a substrate transport container standby station, where a plurality of substrate transport containers according to the first or second aspect of the present invention can stand by and which has charging terminals for automatically starting charging when each of the substrate transport containers is seated in a standby position. Because the secondary battery as a power source for driving the fan motor has only a limited battery capacity, the fan motor cannot be operated in excess of several days. When a plurality of substrate transport containers are seated in predetermined positions, respectively, the secondary batteries mounted in the containers are automatically charged and controlled, thereby allowing the substrates to be stored for a long period of time without manual operation. The standby station also functions as substrate storage equipment.
According to a fifth aspect of the present invention, there is provided a method for maintaining cleanliness of substrates, wherein after the atmosphere in the substrate transport container according to the first or second aspect of the present invention has been replaced with dry air, clean air is circulated through the substrate transport container to provide ventilation. During storage of wafers, a native oxide film grows on the wafers from water and oxygen in the storage environment. After the wafers have been put in the substrate transport container, the air in the container is replaced with dry air to reduce the concentrations of water and oxygen to ultra-low levels. Consequently, it is possible to suppress the growth of a native oxide film. At the same time, it is possible to prevent adsorption of particulate contaminants and organic matter.